The present invention is directed to a fuel composition comprised of sewage sludge and an organic fuel comprised of a liquid hydrocarbon fuel oil.
In an effort to provide an economic and environmentally acceptable method for the disposal of sewage sludge, various municipalities have recently begun to investigate various means to accomplish this difficult task. Disposal of sewage sludge is rapidly becoming a world-wide problem. Many large municipalities on ocean coastlines dump sewage sludge produced by them into the oceans with the consequence of ultimately endangering ocean aquatic life. Inland municipalities frequently employ the sludge as a source of plant nutrients. However, the supply of sewage sludge is rapidly exceeding demand. As a result, the sewage sludge is frequently disposed of by means of landfill. Others employ expensive and involved incineration methods to dispose of their sludge whereby the sludge is first dried to form a combustible solid. Because of the rapid increase in the world population over the last 100 years and the shift from an agrarian-based to urban-based culture, the use and/or disposal of increasing quantities of sewage sludge is rapidly becoming a problem of alarming proportion. Furthermore, toxic and hazardous wastes comprise an important component of sludge, adding to the complexity and safety of current sludge disposal techniques since such components are highly leachable. Therefore, it would be extremely advantageous to provide an economic and environmentally acceptable means of disposal of such sewage sludge by use of incineration, thereby avoiding the problems associated with landfills and ocean dumping.
Various methods have been discussed in the patent literature for the disposal of sewage sludge by incineration. For example, U.S. Pat. No. 4,405,332 (issued to Rodriguez et al) discloses a fuel composition comprised of non-dewatered sewage sludge and a particulate solid fuel such as coal. U.S. Pat. No. 4,026,223 (issued to Robbins) discloses a sludge incinerator for use in the flash evaporation of water contained in high moisture sludges. The patent states at column 2, lines 31-33 that "waste oil or other flammable hydrocarbons may be introduced along with the sludge to aid in the ignition of the sludge." U.S. Pat. No. 4,145,188 (issued to Espenscheid et al) discloses a process for the liquefaction of municipal refuse and other solid organic wastes in a highly aromatic refinery petroleum solvent to provide a liquid fuel. U.S. Pat. No. 4,168,670 (issued to Wall et al) discloses the incineration of lime-conditioned dewatered sewage sludge with a high sulfur fuel such as a fuel oil. British Pat. No. 1,198,958 discloses a solid fuel composition comprised of solid sewage waste, coal tip waste and waste oil.
U.S. Pat. No. 3,559,596 (issued to Ishii et al) is directed to a method and apparatus for the incineration of sewage sludge wherein a sludge is subjected to pressure and heated concurrently and then jetted into a combustion chamber. Water contained in the sludge is evaporated instantaneously with the jetting, with the remaining solids being incinerated. The patent discloses at column 2, lines 62-65 that the sludge-feeding duct is connected to a heavy oil-feeding duct. Example 1 also discloses the admixture of heavy oil with a sludge which is comprised of 80 percent by weight of water. The patent appears to be directed to the use of a partially-dewatered sludge as noted in the Examples (water content of 75-80 percent) and column 1, lines 15-20 wherein the partial dewatering of activated and digested sludge is discussed.
Japanese Patent Publication 55-94996 discloses a slurry fuel which includes particulate coal, oil, sewage sludge and a viscosity-lowering additive. The patent states that the sludge may contain from 30 to 90 percent water. However, the patent generally envisions the use of partially dewatered sludge as it states that the sludge should comprise less than 50 percent by weight of water.
Insofar as various of the above-noted methods are not readily adapted to the commercial environment as they require various secondary treatment processes such as dewatering prior to incineration of the fuel, it would be desirable to provide an improved sewage sludge-containing fuel which may be more simply produced and incinerated.